Several techniques currently exist for treating cells at a selected site in the body with heat or chemicals to kill or impede multiplication of those cells to prevent undesired cell proliferation. For example, numerous types of chemotherapy drugs exists which, when injected into a tumor or delivered systemically to a patient, attack and kill cancerous cells to prevent them from further multiplying.
Radiation techniques can also be used to kill cancerous or other undesired cells. Cell death begins to occur when the cells are heated to a temperature of about 5° C. or more above the normal body temperature of 37° C. Applying radiation to a localized site in the body, such as a tumor or other area containing undesired cells, can heat the cells at the site to temperatures in excess of 60° C. Such high temperatures causes a phenomenon known as protein denaturation to occur in the cells, which results in immediate cell death. Accordingly, radiation therapy has been suitable in successfully treating certain types of cancers and other diseases involving uncontrolled cell growth.
Other types of heating techniques, such as the use of probes or catheters to provide localized heat to a site of interest also exist. Like radiation therapy, these techniques also heat the cells to a temperature sufficient to cause protein denaturation in the cells to thus kill the cells quickly.
Photosensitive chemicals are also used to kill cells at certain sites of interest in the body. For example, a photosensitive chemical can be injected directly into a site of interest to expose cells at that site to the chemical. A light emitting source, which emits light at a wavelength that will activate the photosensitive chemical, is then focused on the site of interest. Accordingly, the light activates the photosensitive chemical that has been absorbed by or is otherwise present in the cells of interest. The activated chemical kills the cells, which thus prevents undesired cell proliferation.
Although the techniques mentioned above can be suitable for preventing certain types of cell proliferation and certain sites in the body, several drawbacks with these techniques exist. For example, often the use of chemotherapy drugs alone to treat a tumor or cancerous site is insufficient to kill the undesired cells. Moreover, the chemotherapy drugs also kill many normal healthy cells along with the cancerous cells, which can adversely affect the patient's health.
The use of radiation in conjunction with chemotherapy can have a more detrimental effect on the cancerous cells. However, as with chemotherapy, radiation often kills normal healthy cells, such as those in front of or behind the site of interest, along with the cancerous cells. Moreover, the intense heating of the cells can cause the cells to coagulate and thus block the capillaries at the site of interest. The blocked capillaries therefore prevent chemotherapy drugs from reaching the site of interest.
One example of a method of chemically treating a target site is disclosed in U.S. Pat. No. 6,248,727 to Zeimer. This method delivers a liposome containing a fluorescent dye and tissue-reactive agent. The liposome is administered intravenously to flow to the locus in the eye of the patient and the site is non-invasively heated to release the dye and the tissue-reactive agent. The dye is fluoresced to observe the pattern of the fluorescence. The tissue-reactive agent is activated to chemically damage and occlude the blood vessel. The liposomes are selected to release the dye at a temperature of 41° C. or less without causing thermal damage to the blood vessel.
In addition, the above techniques have not been used to prevent unwanted cell proliferation at certain locations in the eye, such as at the retina or at the lens capsule, Because the retina is very sensitive, conventional radiation techniques can be too severe to treat cancerous cells on, in or under the retina.
Also, after cataract surgery, a phenomenon known as capsular opacification and, in particular, posterior capsular opacification can occur in which the epithelial cells on the lens capsule of the eye experience proliferated growth. This growth can result in the cells covering all or a substantial portion of the front and rear surfaces of the lens capsule, which can cause the lens capsule to become cloudy and thus adversely affect the patient's vision. These cells can be removed by known techniques, such as by scraping away the epithelial cells. However, it is often difficult to remove all of the unwanted cells. Hence, after time, the unwanted cells typically will grow back, thus requiring further surgery.
Accordingly, a need exists for a method for hyperthermally treating tissue and preventing unwanted cell proliferation at sites in the body, especially at sites in the eye such as the retina, choroid and lens capsule, which does not suffer from the drawbacks associated with the known techniques discussed above.